arch-arm: Fix clasta/b and lasta/b simd&fp instructions
arch-arm: Fix clasta/b and lasta/b simd&fp instructions

The simd&fp version of this instructions required zeroing the result
vector except for the first element, that contains the result.

Change-Id: I231ad3c44d89f34acae26d299ab676e2ed09acdc
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/28247
Reviewed-by: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Maintainer: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5